2,775 research outputs found
How to make large, void free dust clusters in dusty plasma under microgravity
Collections of micrometer sized solid particles immersed in plamsa are used
to mimic many systems from solid state and fluid physics, due to their strong
electrostatic interaction, their large inertia, and the fact that they are
large enough to be visualized with ordinary optics. On Earth, gravity restricts
the so called dusty plasma systems to thin, two-dimensional layers, unless
special experimental geometries are used, involving heated or cooled electrons,
and/or the use of dielectric materials.In micro-gravity experiments, the
formation of a dust-free void breaks the isotropy of three-dimensional dusty
plasma systems. In order to do real three-dimensional experiments, this void
has somehow to be closed. In this paper, we use a fully self-consistent fluid
model to study the closure of a void in a micro-gravity experiment, by lowering
the driving potential. The analysis goes beyond the simple description of the
virtual void, which describes the formation of a void without taking the dust
into account. We show that self-organization plays an important role in void
formation and void closure, which also allows a reversed scheme, where a
discharge is run at low driving potentials and small batches of dust are added.
No hysteresis is found this way. Finally, we compare our results to recent
experiments and find good agreement,but only when we do not take
charge-exchange collisions into account
The effect of thermophoresis on the discharge parameters in complex plasma experiments
Thermophoresis is a tool often applied in complex plasma experiments. One of
the usual stated benefits over other experimental tools is that changes induced
by thermophoresis neither directly depend on, nor directly influence, the
plasma parameters. From electronic data, plasma emission profiles in the
sheath, and Langmuir probe data in the plasma bulk, we conclude that this
assumption does not hold. An important effect on the levitation of dust
particles in argon plasma is observed as well. The reason behind the changes in
plasma parameters seems to be the change in neutral atom density accompanying
the increased gas temperature while running at constant pressure.Comment: 14 pages, 12 figure
Determination of the levitation limits of dust particles within the sheath in complex plasma experiments
Experiments are performed in which dust particles are levitated at varying
heights above the powered electrode in a RF plasma discharge by changing the
discharge power. The trajectories of particles dropped from the top of the
discharge chamber are used to reconstruct the vertical electric force acting on
the particles. The resulting data, together with the results from a
selfconsistent fluid model, are used to determine the lower levitation limit
for dust particles in the discharge and the approximate height above the lower
electrode where quasineutrality is attained, locating the sheath edge. These
results are then compared with current sheath models. It is also shown that
particles levitated within a few electron Debye lengths of the sheath edge are
located outside the linearly increasing portion of the electric field
Experimental and computational characterization of a modified GEC cell for dusty plasma experiments
A self-consistent fluid model developed for simulations of micro- gravity
dusty plasma experiments has for the first time been used to model asymmetric
dusty plasma experiments in a modified GEC reference cell with gravity. The
numerical results are directly compared with experimental data and the
experimentally determined dependence of global discharge parameters on the
applied driving potential and neutral gas pressure is found to be well matched
by the model. The local profiles important for dust particle transport are
studied and compared with experimentally determined profiles. The radial forces
in the midplane are presented for the different discharge settings. The
differences between the results obtained in the modified GEC cell and the
results first reported for the original GEC reference cell are pointed out
Charging and coagulation of dust in protoplanetary plasma environments
Combining a particle-particle, particle-cluster and cluster-cluster
agglomeration model with an aggregate charging model, the coagulation and
charging of dust particles in various plasma environments relevant for
proto-planetary disks have been investigated. The results show that charged
aggregates tend to grow by adding small particles and clusters to larger
particles and clusters, leading to greater sizes and masses as compared to
neutral aggregates, for the same number of monomers in the aggregate. In
addition, aggregates coagulating in a Lorentzian plasma (containing a larger
fraction of high-energy plasma particles) are more massive and larger than
aggregates coagulating in a Maxwellian plasma, for the same plasma densities
and characteristic temperature. Comparisons of the grain structure, utilizing
the compactness factor, {\phi}{\sigma}, demonstrate that a Lorentzian plasma
environment results in fluffier aggregates, with small {\phi}{\sigma}, which
exhibit a narrow compactness factor distribution. Neutral aggregates are more
compact, with larger {\phi}{\sigma}, and exhibit a larger variation in
fluffiness. Measurement of the compactness factor of large populations of
aggregates is shown to provide information on the disk parameters that were
present during aggregation
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How companions speak on patients' behalf without undermining their autonomy: Findings from a conversation analytic study of palliative care consultations
Companions are individuals who support patients and attend health-care appointments with them. Several studies characterised companions’ participation in broad terms, glossing over the details of how they time and design their actions, and how patients and health-care practitioners (HCPs) respond to them. This article aims to examine these aspects in detail by using conversation analysis, focusing on actions whereby companions speak on patients’ behalf—mentioning delicate aspects of patients’ experience (specifically, by alluding to patients’ thoughts or feelings about dying). Some studies suggested that these actions undermine patients’ autonomy. By contrast, through examination of palliative care consultations in a UK hospice, we found that these interventions are warranted by contextual circumstances: they are either invited by patients or HCPs (through questions or gaze) or volunteered to help with the progression of an activity (e.g. when a patient does not answer an HCP’s question). Additionally, all parties collaborate in constructing these companion interventions as temporary departures from an otherwise prevailing normative orientation to patients’ right to speak for themselves. The study contributes to the sociology of health and illness by characterising how companions contribute to the ways in which participants coordinate their relative rights and responsibilities, and ultimately their relationships, within health-care interactions
Metabolic and hormonal studies of Type 1 (insulin-dependent) diabetic patients after successful pancreas and kidney transplantation
Long-term normalization of glucose metabolism is necessary to prevent or ameliorate diabetic complications. Although pancreatic grafting is able to restore normal blood glucose and glycated haemoglobin, the degree of normalization of the deranged diabetic metabolism after pancreas transplantation is still questionable. Consequently glucose, insulin, C-peptide, glucagon, and pancreatic polypeptide responses to oral glucose and i.v. arginine were measured in 36 Type 1 (insulin-dependent) diabetic recipients of pancreas and kidney allografts and compared to ten healthy control subjects. Despite normal HbA1 (7.2±0.2%; normal <8%) glucose disposal was normal only in 44% and impaired in 56% of the graft recipients. Normalization of glucose tolerance was achieved at the expense of hyperinsulinaemia in 52% of the subjects. C-peptide and glucagon were normal, while pancreatic polypeptide was significantly higher in the graft recipients. Intravenous glucose tolerance (n=21) was normal in 67% and borderline in 23%. Biphasic insulin release was seen in patients with normal glucose tolerance. Glucose tolerance did not deteriorate up to 7 years post-transplant. In addition, stress hormone release (cortisol, growth hormone, prolactin, glucagon, catecholamines) to insulin-induced hypoglycaemia was examined in 20 graft recipients and compared to eight healthy subjects. Reduced blood glucose decline indicates insulin resistance, but glucose recovery was normal, despite markedly reduced catecholamine and glucagon release. These data demonstrate the effectiveness of pancreatic grafting in normalizing glucose metabolism, although hyperinsulinaemia and deranged counterregulatory hormone response are observed frequently
Joint Learning of Intrinsic Images and Semantic Segmentation
Semantic segmentation of outdoor scenes is problematic when there are
variations in imaging conditions. It is known that albedo (reflectance) is
invariant to all kinds of illumination effects. Thus, using reflectance images
for semantic segmentation task can be favorable. Additionally, not only
segmentation may benefit from reflectance, but also segmentation may be useful
for reflectance computation. Therefore, in this paper, the tasks of semantic
segmentation and intrinsic image decomposition are considered as a combined
process by exploring their mutual relationship in a joint fashion. To that end,
we propose a supervised end-to-end CNN architecture to jointly learn intrinsic
image decomposition and semantic segmentation. We analyze the gains of
addressing those two problems jointly. Moreover, new cascade CNN architectures
for intrinsic-for-segmentation and segmentation-for-intrinsic are proposed as
single tasks. Furthermore, a dataset of 35K synthetic images of natural
environments is created with corresponding albedo and shading (intrinsics), as
well as semantic labels (segmentation) assigned to each object/scene. The
experiments show that joint learning of intrinsic image decomposition and
semantic segmentation is beneficial for both tasks for natural scenes. Dataset
and models are available at: https://ivi.fnwi.uva.nl/cv/intrinsegComment: ECCV 201
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